Sunday, July 29, 2012

Tea and coffee break

Humans have enjoyed tea and coffee for quite some time. Coffee was being drunk in Europe in the mid-17th century, while tea was supposedly consumed by the Chinese 4500 years ago, although this strongly disputed as the first mention of tea in a Chinese text was only 2000 years ago. Tea arrived in Europe around the same time as coffee. A fascinating history of both beverages can be found in Tom Standage’s [ A history of the world in 6 glasses].
The news is good
Long time readers will remember I have said good things about tea and coffee before, because I prefer a positive food story rather than the scare stories enjoyed by others. It is always comforting to have science on your side. A meta-analysis (Mostofsky 2012) crunched all the research papers between 1966-2011, which included 140,000 coffee drinkers. They concluded: “Moderate coffee consumption is inversely associated with the risk of heart failure, with the largest inverse association observed for consumption of 4 servings per day.” And it didn’t matter whether you’re a boy or a girl.

With four cups of coffee a day there was a 11% lower risk of heart failure. Any benefit was negated once you reached 10 cups a day. The analysis took account of body weight, alcohol consumption and smoking, as is always the way in making sense of research.

And then it gets better
Some scientists who live just down the road from me at the University of Western Australia took a look at both tea and coffee and the potential risk of heart disease (Bøhn 2012). They also were positive about a lower risk of heart disease in tea and coffee consumers after reviewing the published evidence.

Tea seemed to improve the normal functioning of the arterial walls, lower triglycerides, inhibit inflammation and LDL-cholesterol oxidation (the latter two significantly contribute to atherosclerosis) and even lower the risk of stroke. Both tea and coffee are associated with a lower risk of type 2 diabetes. The association seems to be strongest with coffee, possibly due to the chlorogenic acids in coffee.

How much tea and coffee?
Difficult to say precisely, but there is general agreement that 3-5 cups a day is having a useful effect on your health. They did emphasise that genetics could be playing an important role, meaning we can’t say that everyone will benefit from tea and coffee. For example, those with the polymorphism CYP1A2 in the P450 enzyme (that’s laboratory clever people talk I think) are slow caffeine metabolisers, and actually have a higher risk of a heart attack with caffeinated drinks.

All the same, it sounds very encouraging to me.

Is there a “yes, but...?"
Isn’t there always? Generally, the studies rely on self-reported tea and coffee consumption and only one point in time. If you believe that tea and coffee are “bad” then you will probably fib about how much you guzzle, and often people just plain “forget” how much they drink and therefore under-report. Or they may have changed drinking habits over time depending upon what they read in the paper.

Association is not necessarily cause and effect. It could also be that the folk enjoying a brew three or four or five times a day might also eat more vegetables, watch only documentaries, cook proper meals, help their neighbours, give to charity, walk the dog and hug the kids.

Nevertheless, when the numbers are given a thorough massage, it looks like moderate tea and coffee drinkers come out ahead in the health stakes,

What does it all mean?
If you drink tea or coffee, feel very comfortable with the habit. All the evidence suggests that up to five cups a day is fine and may even be a generous leg-up for your health. I suspect that even 6-8 cups a day is OK. Twenty cups? I’m not so sure. Worth considering a cut back. No-one is certain what specific compounds in tea and coffee are responsible for their proposed protection. There are many biologically active compounds, both known and unknown, in tea and coffee.

Between you and I, six cups of tea a day find their way down my throat. They are big cups and I ain’t worried in the slightest. Hopefully, before I die, science will reveal why tea helped me live to 105.

Mostofsky E et al. Circulation Heart Failure 2012; DOI: 10.1161/circheartfailure.112.9672299
Bøhn SK et al. Food & Function 2012 DOI:10.1039/c2fo10288a